1. Field of the Invention
The present invention generally relates to wood products and, more particularly, relates to consolidated cellulosic panels or boards, and apparatus and methods for manufacturing same.
2. Description of Related Technology
During the manufacture of consolidated cellulosic articles, including fiberboard, paperboard, particleboard and the like, wood furnish such as chips, shavings, sawdust, or specially ground fibers, are compressed with a binding agent or resin under heat and pressure. Such boards can be used in a variety of applications including exterior house siding, interior and exterior door facing panels or doorskins, underlayments, garage or workshop paneling pegboard, etc.
The consolidated boards are typically manufactured to a desired face density to, among other things, ensure structural integrity, as well as desirable surface texture, appearance, and paint hold-out characteristics. Examples of consolidated boards and methods of manufacturing same are provided in U.S. Pat. Nos. 3,449,482; 3,661,688; 4,142,007; 4,702,870; and 5,198,236. Such boards must also avoid warping while maintaining such characteristics.
Using the aforementioned door facing panel application as an example, when such door facings are manufactured and shipped, they are often stacked on top of each other. Since there are molded indentations on the top surface of the facing and corresponding protrusions on the bottom surface of the facing, the facings nest together when stacked, with each protrusion registering with an indentation therebelow. The contact point for each top facing upon a corresponding bottom facing occurs between the molded indentations and protrusions. The remaining, unmolded, flat portions of the facings do not contact one another. Such unsupported areas therefore can tend to droop or warp.
For example, if the facings are 0.125xe2x80x2 thick, the space between the flat, unmolded areas in the stacked facings may be 0.040xe2x80x2 thick. If unsupported, such a single facing resting upon a perfectly supported bottom facing could droop 0.040xe2x80x2. However, such facings are typically stacked in groups of 150 facings or more. If each facing is left unsupported, the second from the bottom facing may droop only 0.040xe2x80x2, but the third facing would droop twice that amount, the fourth would droop three times that amount, and so on. For a stack of 150 facings, the top facing may therefore droop close to six inches in the given example.
If the facings could be made to rest with the contact point between facings being the flat unmolded areas then each facing would be fully supported by the facing therebelow and no droop would occur. One way to accomplish this would be to increase the caliper of the flat unmolded areas by a thickness equal to the unsupported space between facings, 0.040xe2x80x2 in the above example. Conventional manufacturing techniques cannot increase the caliper in such a manner without a corresponding decrease in density throughout the resulting board. Such decreases in density result in unacceptable decreases in the paint hold-out characteristic of the board, i.e., the board will absorb paint to an unacceptably high degree, potentially rendering the board unpaintable.
Alternatively, the caliper of the molded indentations and protrusions could be decreased accordingly to allow the flat unmolded areas to fully nest. Such decreases in caliper, however, result in corresponding increases in density. Conventional manufacturing techniques, if used to decrease the caliper to such a degree, would increase the density to a point at which the facings might blister, or otherwise fail.
According to the invention, a method for producing a consolidated cellulosic board includes the steps of providing a first die, providing a second die opposed to the first die, with the second die having a plurality of spaced forms extending toward the first die, positioning a mat of cellulosic material and a binder resin between the first and second dies, with the mat having a first face adjacent to the first die and a second face adjacent to the second die, and compressing the mat between the first and second dies, the first face being compressed to a substantially uniform density, the second face being compressed to a density lower than the density of the first face.
Other aspects of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings and the appended claims.